(1) Field of the Invention
The present invention relates to a method and an apparatus for joining a protective tape to a surface, on which a pattern is formed, of a semiconductor wafer.
(2) Description of the Related Art
Examples of a thin film working method of a semiconductor wafer (hereinafter, also simply referred to as “wafer”) include a mechanical method and a chemical method such as a grinding method, a polishing method (CMP) and an etching method. In these methods, after a protective tape is joined to a surface, on which a wiring pattern is formed, of a wafer, a back grind method for grinding a back surface of the wafer is generally used.
In the back grind method, a surface (pattern surface) of a wafer is suction-held by a holding table, and a back surface of the wafer is ground using a grindstone. Herein, stress is applied to the surface of the wafer due to the grinding operation, and the pattern may be damaged or contaminated in some cases. For this reason, a protective tape is joined to the surface of the wafer.
Generally, a band-like tape is used as the protective tape, an joining roller is allowed to roll on the wafer, and the protective tape is sequentially joined to the surface of the wafer from an end of the wafer. Conventionally, a diameter of the protective tape to be joined to the surface of the wafer is smaller than a diameter of the semiconductor wafer. This is because that if the protective tape is larger than the semiconductor wafer in diameter, when the wafer is subjected to the back grind processing, a portion of the protective tape which comes out or protrudes from the wafer may flap and damage a circumferential end (edge) of the wafer. The protective tape joined to the surface of the wafer in this manner is separated during a separating process after the back grind processing.
However, a semiconductor wafer to which the protective tape is joined and which is subjected to the back grind processing has following problems. That is, a wafer which has been thinned by the back grind processing has an acute edge which projects from the protective tape covering the wafer. Therefore, if the wafer is contained in a cassette, the edge sticks into an inner wall of the cassette. There is a problem that if the wafer is to be taken out from the cassette from such a state, the edge of the wafer is damaged, or a taking-out error is occurred.
The present inventor apply himself closely to the study thereof and, as a result, he performed an experiment in which a protective tape having a diameter larger than that of a wafer is joined to a surface of the wafer and the back grind processing was carried out. As a result, the present inventors found that even when the protective tape protruded from the wafer, the edge or the like of the wafer was not damaged, and patent applications were filed (see JP-A 2003-209082 for example).
According to the above method, the edge or the like of the wafer were not damaged, but since the protective tape having a diameter larger than that of the wafer is used, after the protective tape is cut, an unnecessary portion of the protective tape remaining on an outer circumference of the wafer finely moves vertically when the protective tape is cut. Therefore, there is a new problem that a section of the protective tape joined to the surface of the wafer and a section of the unnecessary protective tape after the protective tape is cut rub against each other and particles are generated. If the wafer is subjected to the back grind processing in a state where the particles are generated on the protective tape surface, a thickness of a portion of the wafer to which the particles are generated is increased, and only this portion is ground thin. As a result, a thickness of a wafer becomes nonuniform and the wafer is damaged.